Conventionally, a heat-pump air-conditioning apparatus including a fin-tube heat exchanger including fins and heat transfer pipes (tubes) has been known. The fins of the fin-tube heat exchanger are arranged at regular intervals and allow a gas (air) to flow therebetween. The heat transfer pipes of the fin-tube heat exchanger are internally grooved, are perpendicularly inserted into each fin, and allow a refrigerant to flow therein.
An air-conditioning apparatus generally includes an evaporator, a compressor, a condenser, an expansion valve, and a four-way valve. The evaporator evaporates a refrigerant and cools air, water, and the like with evaporation heat of the refrigerant. The compressor compresses the refrigerant discharged from the evaporator to a high temperature, and supplies it to the condenser. The condenser heats air, water, and the like with heat of the refrigerant. The expansion valve expands the refrigerant discharged from the condenser to a low temperature, and supplies it to the evaporator. The four-way valve switches between a heating operation and a cooling operation by switching the direction in which the refrigerant flows in a refrigeration cycle. Heat transfer pipes are included in the condenser and the evaporator. A refrigerant containing refrigerating machine oil flows inside the heat transfer pipes.
In recent years, in consideration of rising copper costs, recyclability, and the like, a metal material, such as aluminum or an aluminum alloy, is used to form heat transfer pipes of condensers and evaporators. To attain a high-performance heat exchanger, a technique has been proposed in which a grooved pipe internally provided with straight grooves is used as a heat transfer pipe of the heat exchanger (see e.g., Patent Literature 1). Such straight-grooved pipes have a heat transfer performance better than that of bare pipes. Therefore, when such straight-grooved pipes are used in heat exchangers mounted in an outdoor unit and an indoor unit, the performance of the air-conditioning apparatus can be improved.
Again in recent years, spirally-grooved pipes internally provided with spiral grooves have been developed. With such spirally-grooved pipes, it is possible to achieve a heat exchanger effectiveness higher than that when straight-grooved pipes are used to further improve the performance of the air-conditioning apparatus.